In recent years, with the development of OA appliances and the increasingly widespread use of computers, it is becoming common for ordinary households, personal offices and office units to carry out high-resolution commercial printing such as high-resolution color photograph printing, posters, pamphlets and the like, which conventionally had been done in specialized printing works, and demand is increasing for higher-quality and higher-speed printing techniques.
Such printing techniques that are employed include printing techniques based on electrostatic charge image development, such as electrophotographic methods, electrostatic recording methods and electrostatic printing methods. Generally speaking, fixed images are formed through a plurality of steps in which a photoconductive substance is used to form an electrostatic charge image on a photosensitive body by various means, the electrostatic charge image is then developed with toner, and the toner image is transferred to a print medium such as paper and heated and pressed with a roller to fix the image. The toner remaining on the photosensitive body is cleaned off if necessary by any of various methods and the aforementioned plurality of steps are repeated to accomplish printing.
Recently in the field of electrophotography, there is ever increasing demand not only for higher speed and higher reliability of devices but also for high image quality and color tone for copies that are equivalent to those of printed matter, and there is a need for toner having a high hot offset-generating temperature (excellent hot offset resistance) and excellent image gloss properties (gloss), in order to satisfy such demand. With the increasing importance of energy savings in recent years, it has become a major goal to reduce power consumption in the fixing step, which requires the highest electric power consumption during the electrophotography process. Therefore, toners with low fixing temperatures, i.e. toners with excellent low-temperature fixing properties, are desired.
In the past, polyester resins have been used as binders to improve the low-temperature fixing properties of toners (see Patent documents 1 and 2). Also, binder resins comprising crystalline polyesters and amorphous polyesters have been proposed with the aim of obtaining an excellent low-temperature fixing property (see Patent document 3). In addition, in order to ensure OHP translucency, fixing properties and offset resistance, there has been disclosed an image-fixing method employing color toner comprising, as the binder component, a resin having a number-average molecular weight Mn of 1,000 to 4,000, and a weight-average molecular weight Mw and number-average molecular weight Mn ratio, Mw/Mn, of 45 or greater, as measured by gel permeation chromatography (hereunder, GPC) (see Patent document 4).
On the other hand, as the particle diameter of toner continues to decrease with advancing high image quality, blocking during toner storage has become a problem. With toner having a low fixing temperature, a greater disadvantage is presented in terms of blocking resistance. Research has long been conducted on toner for electrostatic image development exhibiting excellent hot storage properties. For example, for production of chemical toner suited for small toner particle diameters, there has been disclosed a method for producing toner by subjecting an amorphous polyester resin and a crystalline polyester resin dissolved in an organic solvent to phase inversion emulsification in an aqueous medium, and aggregating and coalescing the obtained resin particle dispersion (see Patent document 5).